There exists various load detection devices for a vehicle seat for detecting a load applied by an occupant, to be adapted to a vehicle having an airbag for protecting an occupant seated on the vehicle seat, in order to appropriately adjust gas generation in response to weight of the occupant and in order not to actuate an airbag firing pin in a case where the occupant is a child. For example, disclosed in JP2003-83707A is a strain sensor, in which a bending stress applied to a strain detecting element does not change, thereby enhancing output accuracy.
The strain sensor disclosed in JP2003-83707A is configured so that inner surfaces of a first upper washer contacting an upper surface of a sensor board and a first lower washer contacting a lower surface of the sensor board are press-fitted into a first cylinder, which is press-fitted into a first fixing hole formed at the sensor board, and so that inner surfaces of a second upper washer contacting the upper surface of the sensor board and a second lower washer contacting the lower surface of the sensor board are press-fitted into a second cylinder, which is press-fitted into a second fixing hole formed at the sensor board, and so that inner surfaces of a detector upper washer contacting the upper surface of the sensor board and a detector lower washer contacting the lower surface of the sensor board are press-fitted into a detecting cylinder, which is press-fitted into a detecting hole 14 formed on the sensor board.
As the strain sensor disclosed in JP2003-83707A is configured from the first washer and the second washer, which are separate and independent from each other, two pairs of washers are capable of being press-fitted into the first and second fixing holes of the sensor board via the first and second cylinders, respectively. However, in a case where the first and second washers are integrally connected by means of an attachment portion for attaching, for example, an amplifier thereon, as illustrated in FIG. 2, the two fixing portions (the first and second washers) may not to be press-fitted into the respective holes in the manner disclosed in JP2003-83707A because of a dimensional difference between the two fixing portions and the fixing holes formed at the sensor board or because of a dimensional error. Further, if the two fixing portions are forced to be press-fitted into the corresponding fixing holes, an internal stress is generated at the sensor board and the load may not be accurately detected.
A need thus exists to provide a load detection device which is not susceptible to the drawback mentioned above.